Carlos Esproles

High-efficiency pulsed laser transmitters for deep-space communication

Highly efficient laser sources are required for deep space optical telecommunication. This paper investigates the efficiency components for pulsed diode pumped solid state laser transmitters and determines the overall wall-plug efficiency applicable to a space-borne system. Thermal control of the pump diodes is critical to achieving optimum photon efficiency. Hence, a thermal model involving either a thermo-electric cooler or loop heat pipes is applied to the efficiency calculations. The electro-optical conversion efficiency for an optimized bulk design is expected to be up to 28% with the overall wall-plug efficiency being in the 12 - 16% range depending on the radiator temperature. A fiber based master-oscillator power-amplifier design is also investigated with passively cooled pumped diodes and promises high efficiency operation. Preliminary results from an evaluation model are also discussed.

Tunable frequency stabilized diode-laser-pumped Tm, Ho:YLiF(4) laser at room temperature.

A diode-laser-pumped single-frequency thulium holmium yttrium lithium fluoride laser that exhibits a closed-loop stability of a few megahertz and a continuous single-mode tuning range of 800 MHz is described. The laser output power is 25 mW and is tunable over ~ 8 cm(-1) at 25 degrees C.

Frequency-stabilized diode-pumped Tm,Ho:YLF local oscillator with +4 GHz of tuning range

A tunable, single-frequency, frequency-stabilized, diode- pumped Tm,Ho:YLF laser is described. The laser, which demonstrates the function of a local-oscillator for coherent Doppler lidar in space, has continuous frequency tunability of more than 8 GHz. Active frequency stabilization is achieved by feedback electronics which allow for controlled tuning capability. Output power of more than 20 mW in single-transverse and -longitudinal mode operation with a short term frequency jitter of less than 100 kHz/ms is obtained.

Sub-millimeter laser ranging results using a pseudo-random code modulation

A laser beam with a pseudo random bit stream pattern amplitude modulation is retro reflected off a target to produce a real time ranging signal using a cross correlation technique. The measured resolution of the system was 0.2 mm with an absolute accuracy of ± 2 mm over 2 m. The use of a modulated retro reflector allows a communications signal to be added to the ranging capability.

Automated rejection of parasitic frequency sidebands in heterodyne‐detection LIDAR applications

The authors describe an electronic technique for detecting the sporadic onset of multiaxial mode behavior of a normally single‐mode TEA CO2 laser and demonstrate how this information can be used to facilitate rejection of unsuitable pulses in a heterodyne‐detection LIDAR context.

Frequency monitoring a LIDAR transmitter for pulse‐by‐pulse analysis and control

An electronic technique is described whereby the heterodyne mixing frequency of a pulsed LIDAR transmitter is displayed on a color‐coded linear bar graph. The technique is of great utility for manually fine tuning the laser output frequency when the use of conventional frequency counters and spectrum analyzers is impractical in a rapidly firing system.

Design and performance measurements of an airborne aerosol backscatter lidar

The global winds measurement application of coherent Doppler lidar requires intensive study of the global climatology of atmospheric aerosol backscatter at infrared wavelengths. An airborne backscatter lidar is discussed, which has been developed to measure atmospheric backscatter profiles at CO2 laser wavelengths. The instrument characteristics and representative flight measurement results are presented.